multiple array to json object convert?

In jquery you can use simply like below:

$(a).each(function(n){ab[n]=[a[n],b[n]]; return true;});

for (var i = 0; i < a.length; i++) {
  ab[i] = [a[i], b[i]];
}

underscore has a method called "zip", which performs this task for an arbitrary number of arguments. Here is a rough, not extensively tested implementation:

function zip() {
  if ( ! arguments.length ) {
    return [];
  } 
  var result = [];  
  for (var i = 0; i < arguments[0].length; i++) {
    result[i] = [];
    for (var j = 0; j < arguments.length; j++) {
      result[i][j] = arguments[j][i];
    }
  }
  return result;
}

var ab = zip(a,b);

Kinda late to the party but this should get the job done

2 ARRAYS

  var ab = "",
      a = [1, 2, 3, 4, 5, 6, 7, 8, 9],
      b = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j"],
      x = b.length,
      i = 0;
  for (; i < x; i++) {
      if (typeof a[i] == 'undefined' || typeof b[i] == 'undefined') continue;
      ab += '[' + a[i] + ',"' + b[i] + '"],';

  }
  ab = JSON.parse("[" + ab.substr(0, --ab.length) + "]");

  // ab[0][0] === 1
  // ab[0][1] === 'a'
  // ab[0]    === [1, "a"]
  // ab       === [
  //                [1, "a"],
  //                [2, "b"],
  //                [3, "c"],
  //                [4, "d"],
  //                [5, "e"],
  //                [6, "f"],
  //                [7, "g"],
  //                [8, "h"],
  //                [9, "i"]
  //               ];

Try it at JSFIDDLE

assuming that a and b are the same length this will convert your arrays to json objects.

6 ARRAYS

You can expand your code to accommodate the more arrays like so

  var ab = "",
      a = [1, 2, 3, 4, 5, 6, 7, 8, 9],
      b = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j"],
      c = ["h", "i", "j", "k", "l", "m", "n", "o", "p", "q"],
      d = ["r", "b", "c", "d", "e", "f", "g", "h", "i", "j"],
      e = ["s", "b", "c", "d", "e", "f", "g", "h", "i", "j"],
      f = ["t", "b", "c", "d", "e", "f", "g", "h", "i", "j"],
      x = b.length,
      i = 0;
  for (; i < x; i++) {
      if (typeof a[i] == 'undefined' || typeof b[i] == 'undefined') continue;
      ab += '[' + a[i] + ',"' + b[i] + '","' + c[i] + '","' + d[i] + '","' + e[i] + '","' + f[i] + '"],';

  }
  ab = JSON.parse("[" + ab.substr(0, --ab.length) + "]");

  // ab[0]    === [1, "a", "h", "r", "s", "t"]
  // ab[0][5] === "t" 
  // ab[0][3] === "h"

6 ARRAY FIDDLE

EXPLANATION

We use one loop starting at 0 to the length of one of the array objects, this case b.length. Then for each iteration we convert the values of the array object to a multidimensional string appended to the object ab. While ensuring that the values at each iteration aren't undefined. after the loop we convert the multidimensional string to an JSON object with JSON.parse